Coupons and drug assistance programs have also gained popularity and have made expensive drugs more affordable in some cases. But these programs have their critics: there are signs that they drive up costs in the long run, as they keep patients on branded drugs and defeat healthcare usage barriers inherent in copays, according to a ProPublica report.

To get a better sense of how drug price and insurance issues impacted patient use of DMTs, Wang and colleagues conducted a survey among MS patients in the NARCOMS registry; 6,662 of those contacted responded, which was about a 50% response rate, and the majority of these patients (98.5%) had health insurance.

Yet 22% said their insurance coverage worsened over the past year.

"These negative effects likely reflect the dramatically increased cost of DMTs and the response to those high costs by insurance carriers," the researchers wrote.

About 70% of patients were taking DMTs, and that figure rose to 80% when limited to those with relapsing-remitting MS (RRMS), since the majority of treatments are aimed at this population.

Among those who were not on the drugs, most did so by their own or their physician's choice. Still, some 6% of the patients said they were not on DMTs solely because of insurance or financial reasons, rising to about 9% when restricted to those with RRMS.

Insurance denial was not uncommon, experienced by 3.3% of patients, and 2.3% were denied switching from one therapy to another.

In most cases, the researchers said, physicians were able to appeal those denials and win, although that has an impact on physician time and is not reimbursed, the researchers noted.

They also found that 1.6% of patients either skipped or split doses because of increased costs.

In further analyses, the researchers saw that patients with RRMS who reported a negative insurance change had a significantly increased likelihood of:

Not taking DMTs (OR 1.5, 95% CI 1.16-1.93)

Using free/discounted drug programs (OR 1.89, 95% CI 1.40-2.57)

Encountering insurance challenges (OR 2.48, 95% CI 1.64-3.76)

The study was limited by its use of self-reported data, which can lead to recall and selection bias, but Wang and colleagues still concluded that insurance coverage and rising drug costs negatively affect access to treatment for patients with MS.

In an accompanying editorial, Dennis Bourdette, MD, of Oregon Health and Science University, and Francesco Patti, MD, of the University of Catania in Italy, said that a comparison with European healthcare for MS patients would be helpful, since those governments pay the full price of DMTs and that kind of coverage may increase adherence.

"U.S. neurologists need to speak out about the unfettered rise of MS disease-modifying therapy prices and the obstacles to care created by insurance companies and specialty pharmacies," Bourdette and Patti wrote. "The advancements in the treatment of MS have been remarkable. However, we have much to do in the U.S. to ensure that all people with RRMS receive the full benefits of the transformational advances in the treatment of MS."